The present invention relates generally to endovascular devices for capturing particulate. More particularly, the invention relates to a filter assembly located at the distal end of a delivery member to capture emboli in a blood vessel during a vascular procedure and then remove the captured emboli from the patient after completion of the procedure.
A variety of treatments exists for dilating or removing athersclerotic plaque in blood vessels. The use of an angioplasty balloon catheter is common in the art as a minimally invasive treatment to enlarge a stenotic or diseased blood vessel. This treatment is known as percutaneous transluminal angioplasty, or PTA. To provide radial support to the treated vessel in order to prolong the positive effects of PTA, a stent may be implanted in conjunction with the procedure.
Thrombectomy is a minimally invasive technique for removal of an entire thrombosis or a sufficient portion of the thrombosis to enlarge the stenotic or diseased blood vessel may be accomplished instead of a PTA procedure. Atherectomy is another well known minimally invasive procedure that mechanically cuts or abrades a stenosis within the diseased portion of the vessel. Alternatively, ablation therapies use laser or RF signals to superheat or vaporize the thrombis within the vessel. Emboli loosened during such procedures may be removed from the patient through the catheter.
During each of these procedures, there is a risk that emboli dislodged by the procedure will migrate through the circulatory system and cause clots or strokes. Thus, practitioners have approached prevention of escaped emboli through use of occlusion devices, filters, lysing and aspiration techniques. In atherectomy procedures, it is common to remove the cut or abraded material by suction though an aspiration lumen in the catheter or by capturing emboli in a filter or occlusion device positioned distal of the treatment area.
Prior art temporary filters or occlusion devices are associated with either a catheter or guidewire and are positioned distal of the area to be treated. One prior art collapsible filter device includes a filter deployed by a balloon distal of a dilatation balloon on the distal end of a catheter. The filter consists of a filter material secured to resilient ribs. The ribs are mounted at the distal end of the catheter. A filter balloon is located between the catheter exterior and the ribs. Inflation of the filter balloon extends the ribs outward across the vessel to form a trap for fragments loosened by the dilatation balloon. When the filter balloon is deflated, the resilient ribs retract against the catheter to retain the fragments during withdrawal of the catheter.
Another prior art filter arrangement includes several filter elements fastened in spaced apart arrangement along the length of a flexible elongate member. This forms an open-mouthed tubular sock-like arrangement to capture the emboli within. The filter is collapsed around the flexible elongate member by wrapping it spirally.
Yet another prior art filter includes a filter mounted on the distal portion of a hollow guidewire or tube. A core wire is used to open and close the filter. The filter has an expandable rim at its proximal end formed by the core wire. The filter is secured at the distal end to the guide wire.
Another prior art device has a filter made from a shape memory material. The device is deployed by moving the proximal end of the filter towards the distal end. It is collapsed and withdrawn by sliding a sheath over the filter and then removing the sheath and filter together.
A further prior art filter device discloses a compressible polymeric foam filter mounted on a shaft that is inserted over a guidewire. The filter is inserted collapsed within a housing which is removed to deploy the filter once in position. The filter is retracted by inserting a large bore catheter over the shaft and the filter, and then removing the shaft, filter and catheter together.
Another prior art filter arrangement has a filter comprised of a distal filter material secured to a proximal framework. This filter is deployed in an umbrella manner with a proximal member sliding along the shaft distally to open the filter and proximally to retract the filter. A large separate filter sheath can be inserted onto the shaft and the filter is withdrawn into the sheath for removal from the patient.
Other known prior art filters are secured to the distal end of a guidewire with a tubular shaft. Stoppers are placed on the guidewire proximal and distal of the filter, allowing the filter to move axially and retract independently of the guidewire. A sheath is used to deploy and compress the filter.
A problem associated with known temporary filter arrangements is that emboli may not be fully contained within the filter. Emboli can build up in the area just proximal of the filter, including any frame portion proximal of the filter assembly. As the filter is closed, emboli not fully contained in the filter can escape around the filter into the circulatory system and cause potentially life threatening strokes.
Another known prior art collapsible filter is formed from braided filaments. The pores thus created change in size and shape as the filter expands during deployment or as the filter collapses for removal. However, there are previously unrecognized problems associated with the changing of pore sizes during use of a braided filter. Depending on the braid geometry of the filter, the pore size may increase during the transition of the filter from the expanded, or deployed size to a smaller size required for removal of the filter from the body. This problem is critical during retrieval of the filter when an increase in pore size may allow the escape of embolic material previously captured by the filter.
Therefore, what is needed is a filter arrangement that addresses the problem of emboli not fully contained in the filter assembly. Furthermore, there is a need for a filter assembly that is adaptable for delivery with standard PTCA balloon or stent delivery catheters. Additionally there is a need for a filter arrangement that is secure by being mounted at its distal and proximal ends to the delivery member ensuring proper placement of the filter throughout deployment, capture of the emboli and subsequent removal of the filter and captured emboli. There is also a need for a braided filter with optimal braid geometry to ensure that the pores of the filter do not become larger during removal, when the filter transitions between a deployed size and a collapsed size.
The present invention is a distal protection device for use in vascular procedures. The distal protection device includes a filter assembly adjacent the distal end of a delivery member used in the procedure. The proximal and distal ends of the filter assembly are fixed to the delivery member such that the ends cannot move longitudinally along the delivery member, but may rotate independently of the delivery member core. The filter assembly includes an expandible frame with a distal portion acting as the emboli filter. The emboli filter is sized sufficiently to expand and cover the cross sectional area of the vessel distal of the intended treatment area.
The filter assembly may have a variety of configurations. In one embodiment, the frame consists only of the proximal portion of the filter assembly, with the distal half formed from filter material. The frame can have a braided configuration or consist of a sinusoidal ring element adjacent the filter material with helical segments extending from the sinusoidal ring to the delivery member. In another embodiment, the frame forms a basket arrangement and includes the filter material in the distal half of the basket. Such a frame can be configured with a tighter braid on the distal end, thus obviating the need for a separate filter material. This embodiment may have a generally ovoid shape.
The filter assembly further includes a moveable sheath for positioning the emboli filter between an expanded position and a collapsed position. The sheath extends over the frame, collapsing the frame and filter of the assembly as they are drawn into the sheath. Likewise, when the frame and filter are removed from the sheath, they will expand so that the filter will cover the cross sectional area of the vessel distal of the treatment area.
Alternative embodiments of the filter assembly can include an aspiration lumen and/or a flushing lumen extending through the sheath. This allows large emboli to be lysed or aspirated prior to retracting the filter and removing it from the patient.
Another alternative embodiment of the filter assembly has the proximal end of the filter longitudinally fixed to the delivery member, the distal end of the filter being slidingly attached to the member. When a sheath is passed over the filter to compress it for delivery or retrieval, the distal end of the filter slides distally on the delivery member, extending the length of the filter. The filter of this embodiment may also include a frame that is densely braided to form a basket with fine pores. The filter also has large inlet openings that are formed in the proximal end. The deployed shape of this filter embodiment is generally that of a teardrop, the proximal end having a generally obtuse cone and the distal end having a generally acute cone. A cylindrical well defines the filter body between the proximal and distal cones.
For embodiments that utilize tightly braided frame elements to form the filter medium, the braid geometry is optimized such that the pores only get smaller in size as the filter is collapsed for retraction. In this way, emboli that have been trapped in the braided filter during an endovascular procedure will not escape through the filter orifices as they change shape during the filter withdrawal procedure.
The sheath is configured to be used with either a rapid exchange arrangement or an over-the-wire arrangement as is well known to those skilled in the art.